Production of succinic acid



Patented Mar. 2, 1943 Friedrich Ebel, Mannheim,

Ludwigshafen-on-the-Rhine, Germany;

and Friedrich Pyzik, vested in the Alien Property Custodian No Drawing. Application March 8, 1941, Serial vNo. 382,447. In Germany December 15, 1939 6 Claims.

The present invention relates to the production of succinic acid.

1 The preparation of succinic acid by the oxidation of amber is known. Other known processes for the production of succinic acid consist in the oxidation of cyclobutanol, methylcyclopentene, butylene glycol or furfurol. These processes are ordinarily subject to the disadvantage that the yield of succinic acid is low or that the starting materials are dificultly accessible.

An object of this invention is to provide an im proved method for the manufacture of succinic acid of high purity. We have found that succinic acid may be produced in good yields by sub- Jecting tetrahydrofurane in the liquid phase to an oxidation with higher oxygen compounds of nitrogen. In the practice of our invention, we may employ as the oxidation agent either nitric acid or the higher oxides of nitrogen, e. g., nitrogen dioxide or tetroxide.

when working with nitric acid as the oxidizing agent it is preferable to operate at normal or slightly elevated temperatures. High temperatures should be avoided in order to prevent the further oxidation of succinic acid. When Using, from 50 to 75 per cent nitric acid, the most suitable reaction temperature is within the range from 20 to 40 C., that is below the boiling point of nitric acid. When conducted in this way, the reaction is quite rapid and smooth provided that the concentration of nitric acid is not allowed to become very low. This may be easily attained by providing such an amount of from 50 to 75 per cent nitric acid that the final concentration thereof, 1. e., the concentration after having filtered 03 the succinic acid, is at least 15 per cent. From this acid, a further amount of succinic acid may be obtained by evaporating the acid, preferably at sub-atmospheric pressure, whereby the nitric acid is concentrated. It then may be used for another batch, if necessary after the addition of highly concentrated nitric acid. Nitric acid of low concentration may also be used as oxidizing agent. In this case the reaction is advantageously carried out at temperatures ex-. ceeding 40 C. This method of working, however, is more expensive because a substantial part of this succinic acid remains dissolved in the mother liquor.

The reaction is advantageously carried out in the presence of small amounts of nitrous acid which is usually present in nitric acid. When using nitric acid free from nitrous acid, we prefer to add a small amount thereof before starting the oxidation.

The oxidation with nitric acid may be carried out under reduced pressure, if desired while leading through the solution a ample of nitrogen, carbon dioxide or air. Water or dilute nitric acid are thus removed in an increased amount, thereby withdrawing heat evolved in the oxidation from the liquid reaction mixture. This method makes it possible to maintain the reaction temperature without 'external cooling, while at the same time the water formed in the oxidation is wholly or partly removed in the course of the reaction. Additional concentration of the spent nitric acid may be thu dispensed with. 7

It is possible to carry out the process continuously by allowing such an amount of nitric acid and tetrahydrofurane to flow into the reaction vessel that the most favorable nitric acid concentration is maintained. The vapors emerging from the vessel are preferably condensed in fractions and the nitric acid contained therein recovered for further use.

The reaction may be carried out in the presence of oxidation catalysts, e. g., compounds of iron, manganese, vanadium or chromium.

The conversion of tetrahydrofurane into succinic acid with the aid of higher oxides of nitrogen is likewise preferably carried'out in the liquid phase at normal or moderately elevated temperatures. Tetrahydrofurane or a solution thereof in a suitable inert solvent, e. g., water, dilute nitric acid or glacial acetic acid, may be allowed to flow slowly into liquid nitrogen tetroxide, or gaseous nitrogen dioxide is led throgh liquid tetrahydrofurane or a solution thereof. Nitrogen monoxide and lower oxides of nitrogen do not oxidize tetrahydrofurane. The reaction may also be carried out in the presence of catalysts, if desired under increased pressure.

In one method of carrying out our invention a mixture of nitrogen dioxide and oxygen is introduced into liquid tetrahydrofurane or a solution thereof. The gaseous mixture is most suitably led in a cycle while adding from time to time or continuously fresh oxygen and nitrogen dioxide depending on the rate at which they are used up or converted into nitrogen or lower nitrogenoxides which cannot be regenerated to form nitrogen dioxide. By using an excess of oxygen the formation of nitrogen and of protoxide of nitrogen may be decreased.

The nitrous acid which is added to the nitric acid before oxidation or formed from nitric acid in the course of the oxidation may form a mixture of nitrogen monoxide and nitrogen dioxide,

gas current, for exthe latter being wholly or partly rendered useful for the oxidation. The gases emerging from the oxidation mixture, therefore, contain a preponderating amount 01 nitrogen monoxide which may be converted in known manner" to nitric acid, after having added thereto oxygen or air. It may also be converted into nitrogen dioxide by means of oxygen or air and then used again for the purposes 01' our invention. In this method 01' carrying out the invention, oxygen may be regarded as the oxidizing agent.

The following examples will further illustrate how our present invention may be carried out in practice. It is, however, not restricted to these examples. The parts are by weight.

Example 1 1 part of 94 per cent tetrahydrofurane is allowed to flow slowly into a mixture of 6.62 parts of 65 per cent nitric acid and 0.04 part of sodium nitrite. The temperature of the reaction mixture is maintained at between 20 and 25 C. by external cooling. During the reaction nitrogenous gases are formed which are again converted into nitric acid. When the addition of tetrahydrofurane is finished, the reaction mixture is stirred for some hours and the crystals precipitated are-filtered oil? by suction. The succinic-acid thus obtained is washed with a small amount of water and dried. The yield amounts,

It may then be used again for oxidation, thereby rendering useful the succinic acid contained in the mother liquor.

Example 2 A solution oi? 1 part 01' tetrahydroiurane in 1.4 parts of water is allowed to flow slowly into 3.06 parts of nitrogen tetroxide, while stirring. The temperature is kept below 20. C. by cooling. After having added the tetrahydrofurane, the whole is stirred for some hours until the crystallization is finished. The crystals are filtered off by suction and washed with water. 1.55 parts of succinic acid are thus obtained; a further 0.08- part may be obtained from the mother liquor. The total yield is nearly 100 per cent.

Example 3 Nitrogen dioxide or a mixture of nitrogen dioxide with air or oxygen containing from 20 to 40 per cent of nitrogen dioxide is led through a solution 'of tetrahydrofurane in an equal amount of water or 20 per cent nitric acid. The temperature is maintained between 20 and 50 0., preferably at 30 C. by cooling. When heat is no longer evolved, the mixture is allowed to cool and the succinic acid formed is filtered off by suction. ,A fresh amount of tetrahydroiurane is added to the flltrate,.and the solution obtained is again subjected to oxidation in the manner described. The yield is about 100 per cent.

The nitrogen dioxide or the mixture containing it may also be led in a cycle.

What we claim is:

1. A process for the production of succinic acid which consists in subjecting tetrahydrofurane in the liquid phase to oxidation by a nitrogenous oxidizing agent selected from the group consisting oi! nitric acid and higher oxides ofnitrogen.

2. A process for the production of succinic acid which consists in subjecting tetrahydrofurane in the liquid phase to oxidation by nitric acid.

3. A process for the production of succinic acid which consists in introducing liquid tetrahydrofurane into nitric acid of from 50 to per cent strength at temperatures between 20 and 40 C.

4. A process for the production of succinic acid which consists in introducing liquid tetrahydrofurane into such an amount of nitric acid of from 50 to 75 per cent strengthat tempera-- tures between 20 and 40 C. that at the end of the oxidation the reaction mixture contains at least 15 per cent of nitric acid.

5. A process for the production or succinic 5 acid which consists in introducing gaseous nitrogen dioxide into liquid tetrahydrofurane.

6. A process for the production of succinic acid which consists in introducing a gaseous mixture of nitrogen dioxide and oxygen into an aqueous solution 01' tetrahydrofurane.

FRIEDRICH EBEL'. FRIEDRICH PYZIK. 

